#bigbox{
	width: 1000px;
	height: 1000px;
	border: 2px solid black;
	margin-left: auto;
	margin-right: auto;
	/*无positon定义的外框架，box将基于整个body进行绝对定位操作*/
}

#box1{
	width: 100px;
	height: 100px;
	background: red;
}

#box2{
	width: 100px;
	height: 100px;
	background: green;
	position: absolute;
	top: 10px;
}

#box3{
	width: 100px;
	height: 100px;
	background: blue;
}
